Branches Of Different Lengths Research Articles

Seedless, size and shape controlled synthesis of gold mesoscopic particles and their excellent SERS applications

Development of facile synthesis strategies for complex-shaped gold nanostructures have great significance owing to their prospective applications. Herein, we demonstrate a remarkably simple single-step recipe for the synthesis of micrometer sized gold particles with tailored nanostructured surfaces. We demonstrate that gold micro-particles (GMPs) can be synthesized simply by mixing HAuCl4, cetyltrimethylammonium bromide (CTAB), AgNO3 and ascorbic acid (AA), without the seed particles. This is contrary to the conventional belief that HAuCl4 cannot be completely reduced by AA in the presence of high concentration of CTAB. The surface morphology of GMPs can be tuned by changing the concentration of AA, whereas the size of the GMPs can be controlled by tuning the concentration of CTAB in the reaction medium. The GMPs have shown excellent potential for SERS applications. The simulation results show that each GMP has high concentration of intraparticle hotspots. The finite element simulation shows maximum enhancement factor in excess of 109, while the average experimental enhancement factor can be as high as 4 × 107. The simulation results also indicate that the presence of branches of different lengths enable GMPs to show efficient SERS sensing for multiple excitation sources. Therefore, GMPs have the capability to become universal SERS platforms.

A Printed Wideband Squintless Traveling-Wave Antenna

In this letter, a printed wideband squintless traveling-wave antenna is proposed. The antenna is composed of a transmission line, which is loaded with a set of bent branches that are connected to radiators. With branches of different lengths, the main beam can be designed in an arbitrary direction between the backfire and the endfire. Compared with previously published squintless linear array antennas, the proposed antenna owns a novel arrangement of branches, which is compact especially when there are a large number of radiators. The working principle is explained and a prototype of a 16-branch antenna is fabricated for validation. The measurement results show that the direction of the main beam is fixed at 30° ± 2° (measured from the broadside direction) in the range of 9.0-14.0 GHz (with a radiation bandwidth of 43.5%) and the peak gain is 11.0 dBi.

Alter macrophage adhesion and modulate their response on hydrophobically modified hydrogels

• Facile modification of naturally derived polymers to increase hydrophobicity. • Hydrogels were crosslinked via in situ thiol-ene chemistry. • Protein adsorption and macrophage proliferation increased on hydrophobic hydrogels. • Macrophages pro-inflammatory response was suppressed on hydrophobic hydrogels. Adhesion of macrophages to material substrates plays an essential role in many biological behaviors and biomedical procedures, including wound healing, cancer treatment and biomaterial implantation. Therefore, altering the adhesion of macrophages using biomaterial design may help control their biological function. In this work, we developed a straightforward method to render the hydrogel surface more hydrophobic and demonstrated that the adhesion of macrophages on hydrogels was enhanced on these more hydrophobic surfaces. Compared to the unmodified methacrylated gellan gum (MGG) hydrogel, the water contact angle increased and the swelling ratio decreased for modified MGG hydrogels. The degree of hydrophobicity was controlled by attaching hydrophobic branches of different lengths to the MGG, while the modification did not change the hydrogel compressive modulus. This ensured that the observed different cell responses were mainly due to hydrophobicity change and not the mechanical property difference among the hydrogels. Cell (RAW 264.7 macrophages) proliferation and spreading increased with increasing surface hydrophobicity. Protein adsorption on hydrogel surfaces showed the same trend. Quantification of adhesion to hydrogel surfaces using a hydrophobic probe showed that adhesion was enhanced as substrate hydrophobicity increased. This suggests that cell adhesion may be promoted due to the increase in hydrophobic adhesion that could enhance protein adsorption. In addition, tumor necrosis factor-α (TNF-α) secretion by lipopolysaccharide (LPS) activated M1 and interleukin-4 (IL-4) activated M2 macrophages was also altered by substrate hydrophobicity. TNF-α production, a marker of pro-inflammatory macrophages, decreased with substrate hydrophobicity. These results suggest that substrate hydrophobic can be used to modulate macrophage responses.

Macrophage Adhesion and Phenotypic Shifts on Hydrophobically Modified Hydrogels

A balance of macrophage phenotypes is essential in successful implantation. Therefore, biomaterials should be carefully designed to better regulate the response of macrophages. We demonstrate macrophage adhesion and phenotypic shifts can be modulated with hydrophobically modified hydrogels. This study represents a fundamental concept in controlling cell adhesion and differentiation with substrate hydrophobicity. Gel synthesis was carried out using methacrylated gellan gum (MGG), which was polymerized and crosslinked through a photo-initiated thiol-ene reaction in situ. The degree of hydrophobicity was controlled by attaching hydrophobic branches of different lengths to the MGG. The attachment was carefully controlled so that the hydrogel compressive modulus was not affected by the hydrophobic modification. Compared to unmodified MGG, the water contact angle increased and the swelling ratio decreased for modified MGG hydrogels. Naive and activated macrophages were subsequently seeded on the hydrogels with different surface wettability. Cell proliferation and spreading increased with increasing surface hydrophobicity. Hydrogel surface adhesion to a hydrophobic probe was quantified and showed an increasing trend with increasing substrate hydrophobicity. This suggests that the hydrophobic surface may increase protein adsorption, which, in turn, increases cell spreading. Cytokine secretion by M1 and M2 macrophages were also altered by substrate hydrophobicity. Both nitrite production, a marker of M1, and urea production, a marker of M2, increased with substrate hydrophobicity, with nitrate production being more pronounced. RAW 264.7 macrophages seeded on these substrates shifted to a more pro-inflammatory phenotype with increasing substrate hydrophobicity.

Coplanar waveguide fed dual‐band dual‐sense circular polarized square slot antenna

A novel design of a dual-band dual-sense circularly polarized square slot antenna with two rectangular shaped parasitic patches etched on a single substrate for 1.74/2.82 GHz applications is presented. A coplanar waveguide (CPW) fed line with two horizontal branches of different lengths is used, which produce two different frequencies bands. However, good circular polarization (CP) performance is achieved by adjusting the size of the parasitic patches. The two branches of feed line can excite dual-band dual-sense circular polarized wave. The antenna generates right hand circular polarization (RHCP) and left hand circular polarization (LHCP) radiation at 1.74 and 2.82 GHz, respectively. Lower band is obtained due to 90° phase difference between currents in the two orthogonal branches of the feed line. The lower band of CP is controlled by the size of parasitic patch/element (PE2) and the upper band of CP is controlled by length of right-sided horizontal branch of feed line. The key parameters of the design are investigated to show how to obtain dual CP with impedance matching.

Prediction of Microdroplet Breakup Regime in Asymmetric T-Junction Microchannels.

Splitting droplets is becoming a major functional component in increasing number of droplet microfluidic applications, and there is an increasing interest in splitting droplets into two daughter droplets with different volumes. However, designing an asymmetric droplet splitter and predicting how a droplet splits in such designs is not trivial. In this study, numerical simulations were conducted to study droplet breakup in asymmetric T-junctions of square cross-sections having different pressure gradient ratios (i.e. T-junctions with outlet branches of different lengths). The goal of the simulation is to identify the conditions where a parent droplet breaks or does not break into two smaller droplets of different sizes (so called critical condition) and to identify the important fluid and microchannel parameters in this process. Four modes of droplet breakup (primary-, transition-, bubble-, and non-breakups) are identified and an empirical correlation is introduced that can predict the breakup/non-breakup of the droplet based on the parent droplet size and the capillary number. The simulation results are then compared with experimental data to verify its accuracy and the effect of fluids properties on the proposed correlation are studied. Two major asymmetric breakup mechanisms are determined, namely "breakup with permanent obstruction" and "unstable breakup". The numerical results show that the splitting ratio for the asymmetric breakup mechanisms depends on flow conditions and dwell time of the droplet at the junction prior to splitting. Finally, the results from two-dimensional and three-dimensional simulations were compared. It is shown that two-dimensional simulation may not accurately predict the breakup behavior for asymmetric droplet breakup and viscosity ration has a greater effect on the prediction critical condition.

Design and fabrication of simple and frequency-adjustable dual-band and triple-band antennas

A novel dual-band antenna and a triple-band monopole antenna were developed and fabricated on an Al2O3 ceramic substrate with a thickness of 0.4 mm. An L-shaped electrode structure with two branches of different lengths was designed for the antenna with two resonant frequencies, and a W-shaped structure with triple branches of different lengths was designed for the antenna with three resonant frequencies. The two antennas had simple structures, and the resonant frequency could be easily adjusted by changing the length of each branch. A stub was added to both antennas at the input microstrip line to control the input impendence, which gave the antennas better radiation (S11) properties. For the L-shaped antenna, the designed dual resonant frequencies were 2.4 and 3.5 GHz and for the W-shaped antenna, the designed triple resonant frequencies were 2.4, 3.5, and 5.7 GHz. The lengths of the radiation lines, the length of the ground plane, and the length between the tuning stub and the two radiation lines were used as design parameters. Different design parameters were changed to determine how this would affect the antennas’ characteristics. We found that the different parameters had large effects on the return loss (S11) value, and that stub length had a large effect on the resonant frequencies and return loss values.

Suppression of Phonon Transport in Molecular Christmas Trees.

Minimising the phonon thermal conductance of self-assembled molecular films, whilst preserving their electrical properties, is highly desirable, both for thermal management at the nanoscale and for the design of high-efficiency thermoelectric materials. Here we highlight a new strategy for minimising the phonon thermal conductance of Christmas-tree-like molecules composed of a long trunk, along which phonons can propagate, attached to pendant molecular branches. We demonstrate that phonon transport along the trunk is suppressed by Fano resonances associated with internal vibrational modes of the branches and that thermal conductance is suppressed most-effectively in molecules with pendant branches of different lengths. As examples, we use density functional theory to demonstrate the reduction in phonon transport in tree-like molecules formed from alkane or acene trunks with various pendant branches.

First Report of Root Rot and Crown Necrosis Caused by Pythium aphanidermatum on Phaseolus vulgaris in Oman.

In March 2013, 90% of mature bean plants (Phaseolus vulgaris L. cv. Kendo) grown on a commercial farm in the north of Oman (Barka) developed symptoms of root rot and necrotic streaks on the crown area of the stem and wilted. A Pythium spp. was isolated consistently from roots and basal stems on 2.5% potato dextrose agar (PDA) and V8 (100% vegetable juice) plus 1.5% agar technical. Colonies of Pythium spp. on PDA and V8 plus agar developed abundant aerial mycelia, with the main hyphae being up to 10 μm wide. Zoosporangia were made up of terminal complexes of swollen hyphal branches of different lengths and up to 22 μm wide. Oogonia were terminal, globose, and smooth with a 26-μm diameter (average of 20). Antheridia were mostly intercalary, sometimes terminal, and broadly sac-shaped, 15 μm long and 11 μm wide (average of 20). Oospores were aplerotic, 23 μm in diameter (average of 24), with walls 1 to 2 μm thick at 25°C (ambient temperature). The internal transcribed spacer of the ribosomal DNA (ITS1 and ITS4) sequence of the isolates matched the sequence of Pythium aphanidermatum (Edson) Fitzp. in GenBank. The sequence of isolate Py1 was deposited in GenBank as Accession No. KM102739. This isolate was identified as P. aphanidermatum on the basis of morphological and cultural characteristics (1) and the ITS rDNA sequence. The ITS was found to share 100% nucleotide similarity to previously published sequences of the ITS (KJ755088). To fulfill Koch's postulate, a 5-mm plug of 5-day-old mycelium of isolate Py1 grown on 2.5% PDA was used to inoculate healthy seedlings of beans cv. Kendo. The plug was placed adjacent to the bean stem; PDA served as a control. Five replicate plants were used for the treatment and the control. The plants were maintained in a glasshouse at a temperature of 23 to 25°C. The plants were watered every day. The irrigation water had an electrical conductivity value of 0.2 dSm-1. Eleven days after inoculation, 90% of the plants developed root rot, crown necrosis, and wilt symptoms similar to those observed in the field. On the other hand, control plants did not show any symptoms. The pathogen was re-isolated from roots and basal stems of symptomatic plants. To our knowledge, this is the first report of P. aphanidermatum as the causal agent of root and crown necrosis of mature bean plants in Oman. Future studies should focus on evaluating management options for this disease to avoid possible losses in a crop that has a high export value in Oman. Reference: (1) Y. Serrano et al. Plant Dis. 92:174, 2008.

A multiarm curl antenna for GPS applications

A single-feed dual-band antenna with wide-beam circularly polarized (CP) radiation is introduced for application in the global positioning system (GPS). The primary radiating element is a planar multiarm curl antenna. The dual-band operation is achieved by dividing the arms of the antenna into two branches of different lengths. To generate CP radiation, the radiator is fed by double vacant-quarter printed rings, which allows direct matching of the antenna to a single 50 Ω coaxial line. To enable unidirectional CP radiation and improve the 3 dB axial ratio (AR) beamwidth, the planar multiarm curl radiator is backed by a rectangular cavity-backed reflector. The final design, with an overall GPS-L2 frequency size of approximately λo/2.45 × λo/2.45 × λo/8, resulted in a |S11|<–10 dB bandwidth of 1.221–1.282 GHz (4.9%) and 1.546–1.660 GHz (7.1%) and a 3 dB AR bandwidth of 1.212–1.240 GHz (2.2%) and 1.560–1.590 GHz (1.9%). Furthermore, it showed excellent right-hand CP (RHCP) radiation at both operating bands, namely wide beamwidth, similar gain, a high front-to-back ratio, and high radiation efficiency.

Bent-core luminescent and electroactive bis(triazolyl)triazines with compact columnar mesomorphism

The bulk self-assembly of bent-core molecules based on the novel structure 2-methoxy-4,6-bis(1′,2′,3′-triazol-4′-yl)-1,3,5-triazine is reported together with their luminescent and electrochemical properties. Two families of compounds with lateral branches of different lengths have been investigated. Columnar mesomorphism with short stacking distances and periodic twisted structures were found. A compound exhibiting two hexagonal columnar mesophases that show different emission spectra and a transition from a bimolecular assembly to a unimolecular assembly is described.

Wide-Beam Circularly Polarized Crossed Scythe-Shaped Dipoles for Global Navigation Satellite Systems

This paper describes composite cavity-backed crossed scythe-shaped dipoles with wide-beam circularly polarized (CP) radiation for use in Global Navigation Satellite Systems. Each branch of the dipole arm contains a meander line, with the end shaped like a scythe to achieve a significant reduction in the size of the radiator. For dual-band operation, each dipole arm is divided into two branches of different lengths. The dipoles are crossed through a 90° phase delay line of a vacant-quarter printed ring to achieve CP radiation. The crossed dipoles are incorporated with a cavity-backed reflector to make the CP radiation unidirectional and to improve the CP radiation beamwidth. The proposed antennas have broad impedance matching and 3-dB axial ratio bandwidths, as well as right-hand CP radiation with a wide-beamwidth and high front-to-back ratio.

Are structural properties of dendrimers sensitive to the symmetry of branching? Computer simulation of lysine dendrimers

Poly-L-lysine (PLL) dendrimers are promising systems for biomedical applications due to their biocompatibility. These dendrimers have a specific topology: two spacers of different lengths come out of each branching point and thus the branching is asymmetric. Because of this asymmetry terminal groups are located at branches of different lengths, unlike dendrimers with a symmetric branching. This paper presents the results of the first systematic molecular dynamics simulation of such asymmetric PLL dendrimers. It is shown that PLL dendrimers are porous molecules with all terminal groups equally accessible to water. We have found that in spite of an asymmetry of branching the general structural characteristics of PLL dendrimers are rather similar to those of dendrimers with symmetric branching. We have also found that the structural characteristics of PLL dendrimers obey the general laws for dendrimers and that their electrostatic properties agree with the predictions of a general analytic theory.

Thermal and viscoelastic structure–property relationships of model comb-like poly(n-butyl methacrylate)

A range of comb polymers of poly(n-butyl methacrylate), where the degree of polymerization (DP) of both the backbone and branches was controlled using RAFT-mediated free-radical polymerization, was synthesized using the method of Vosloo et al. [Macromolecules 2004;37: 2371]. Individual architectural parameters (branch length, branch number and DP of the comb backbone) of these relatively monodisperse samples were systematically varied in order to study the impact of each structural parameter on the thermal and rheological properties of the resulting comb polymers. Differential scanning calorimetry showed lower glass transition temperatures for the comb polymers compared to the original linear backbones. There were negligible differences in glass transition temperatures between comb polymers containing branches of different lengths, and between comb polymers containing backbones of narrow and of broad molecular weight distributions. These observations suggest that because the comb polymers are very tightly spaced, the branches act in the same way as long chain polyBMA. Viscoelastic properties of the comb polymers were investigated using dynamic mechanical analysis, using time–temperature superposition to extend the rheological data over a wide frequency range. Major differences in the viscoelastic responses of the original linear backbones and the comb polymers were observed, which were explained in terms of arm retraction/relaxation leading to tube dilation. All comb polymers showed viscoelastic responses that are characteristic of combs, but differences in responses due to changes in branch length and branch number were difficult to detect. This was mainly due to the relatively high number of branches, whose retractions occurred over a broad frequency range, and thus dominated the observed changes in moduli, thereby possibly masking subtle differences in responses.

Transmittance anomalies of a ring with lead-positional asymmetry

We examine the anomalous behavior of the transmittance through a one-dimensional ring having two branches of different lengths, as determined by the lead positions. Jumps in the transmittance phase are occurring in correspondence to both (a) zeros in the transmission at the eigenstates of the isolated ring and (b) destructive interference events. It is also found that when the ratio of the branch lengths is given by p/q satisfying p + q = 0 (mod 4), the two characteristic zeros merge into a single point and the transmittance phase becomes identical to the so-called Friedel phase.

Roles of Branch Content and Branch Length in Copolyethylene Crystallization: Molecular Dynamics Simulations

Molecular dynamics simulations of two series of single copolymer chain models with precisely controlled methyl branching and with branches of different lengths are performed. For the models with precisely controlled methyl branching, the collapse process and the morphology of the lamellar structure are similar to those of the random copolymer. In particular, it is found that the branch content plays an important role in determining whether a single chain can form a lamellar structure or not. With the decrease of the branch contents, more perfect lamellar structure is formed, and the crystallinity of the copolymer increases. For the models with branches of different lengths, the simulations show that the branch point (CH unit) is always expelled from the crystalline phase as a defect, while the behavior of the branch chain in the crystallization depends on the chain length. When the chain has less than 10 carbon atoms, the branch is rejected to the folded surface of the lamellar structure as a defect, whereas when the branch length is longer, the branch is folded back and cocrystallizes with the main chain. In this case, the branch chain is packed in a manner as in polyethylene.

Quantal secretion and nerve-terminal cable properties at neuromuscular junctions in an amphibian (Bufo marinus).

The effect of a conditioning depolarizing current pulse (80-200 micros) on quantal secretion evoked by a similar test pulse at another site was examined in visualized motor-nerve terminal branches of amphibian endplates (Bufo marinus). Tetrodotoxin (200 nM) and cadmium (50 microM) were used to block voltage-dependent sodium and calcium conductances. Quantal release at the test electrode was depressed at different distances (28-135 microm) from the conditioning electrode when the conditioning and test pulses were delivered simultaneously. This depression decreased when the interval between conditioning and test current pulses was increased, until, at an interval of approximately 0.25 ms, it was negligible. At no time during several thousand test-conditioning pairs, for electrodes at different distances apart (28-135 microm) on the same or contiguous terminal branches, did the electrotonic effects of quantal release at one electrode produce quantal release at the other. Analytic and numerical solutions were obtained for the distribution of transmembrane potential at different sites along terminal branches of different lengths for current injection at a point on a terminal branch wrapped in Schwann cell, in the absence of active membrane conductances. Solutions were also obtained for the combined effects of two sites of current injection separated by different time delays. This cable model shows that depolarizing current injections of a few hundred microseconds duration produce hyperpolarizations at approximately 30 microm beyond the site of current injection, with these becoming larger and occurring at shorter distances the shorter the terminal branch. Thus the effect of a conditioning depolarizing pulse at one site on a subsequent test pulse at another more than approximately 30 microm away is to substantially decrease the absolute depolarization produced by the latter, provided the interval between the pulses is less than a few hundred microseconds. It is concluded that the passive cable properties of motor nerve terminal branches are sufficient to explain the effects on quantal secretion by a test electrode depolarization of current injections from a spatially removed conditioning electrode.

Complexation of poly(methyl methacrylate-g-ethylene oxide) with potassium picrate by the extraction technique

Poly(methyl methacrylate) copolymers grafted with poly(ethylene oxide) were synthesized by reaction of methyl methacrylate and methacrylate-headed poly(ethylene oxide) macromonomer. Copolymers with branches of different lengths and different contents were obtained. The complexation efficiency in solution of the polymers with potassium picrate was investigated by means of the extraction with immiscible solvents technique.

ANALYSIS OF TRANSIENT PRESSURES IN TWO-COMPONENT TWO-PHASE FLOW

In this paper, the problem of hydraulic transients resulting from valve closure in a branched pipe carrying a two-component, two-phase flow is theoretically investigated. The governing equations were derived on the basis of one dimensional flow. The method of characteristics was used for solving the resulting differential equations. The evaluation of time interval was made in such a way to be suitable for use in a branched pipe system having branches of different lengths. The analysis of many investigated cases reveals that the maximum pressure rise increases with the increase of the delivery pipeline diameter and with the decrease of valve closure time and void fraction. Moreover the study shows that in all investigated cases, the lowest value of maximum pressure rise occurs when the piping lengths ratio C branched dead end pipe to upstream pipe lengths ) approaches unity.

Bathymetric adaptations of reef-building corals at davies reef, great barrier reef, Australia. I. Long-term growth responses of Acropora formosa (Dana 1846)

In situ rates of linear growth (branch extension) were measured for Acropora formosa (Dana) at depths of 5, 10, and 15 m. Estimates of radial branch growth and internal accretion were made at the shallowest and deepest sites. In addition, reciprocal transplant experiments between these two sites were conducted using branches of different lengths. The in situ results showed that individual branches at the deep site extended twice as fast, and deposited more calcium carbonate than branches at the shallow site. Branch initiation, however, was more rapid at the shallow site. Thus, if the extension of new lateral branches were included to obtain a measure of overall growth, rates were highest at the shallow site. The initial length of the transplanted branches significantly affected growth rates. Longer branches showed greater overall growth within all treatments. Branch extension rates, however, increased with initial branch length at the deep site, while tending to remain constant at the shallow site. This result is interpreted as evidence that the extension of each branch tip at the deep site was supported by translocated metabolites derived from a greater volume of zooxanthellae-bearing tissue than at the shallow site. A. formosa exhibits different growth patterns at different depths. At the deep site, extension is favoured over branch initiation. Consequently, translocation from a greater volume of tissue is presumably available to sustain the higher extension rate at each tip. At the shallow site, where extension is less rapid but branch initiation is more rapid, each tip probably receives translocate from a smaller volume of tissue. These mechanisms result in different growth forms at the two sites and are apparently adaptations to different environmental conditions. Light or water motion, or a combination of the two are proposed as probable controlling factors.